The subject invention concerns a novel use for melatonin to regulate the uterine environment in an animal for enhanced pregnancy success.
Melatonin has been administered in the past to treat a variety of ailments and is currently in common use in humans for regulation of biorhythms, including light-dark cycle regulation in treating depression and for treating disrupted sleep patterns, or xe2x80x9cjet-lag,xe2x80x9d which can result from long-distance travel across time zones. Melatonin, or a derivative thereof, has also been described as being useful as a treatment for breast or other cancers.
It has been recognized that progesterone levels increase following administration of melatonin to certain animals, including sheep and marmosets. For example, Wallace et al. ([1988] J Endocr. 119:5-523-530) stated that melatonin orally administered to ewes increased plasma progesterone concentrations. However, the conclusion as to the effect of melatonin on the corpus luteum and improvements in conception rates were xe2x80x9cequivocal.xe2x80x9d See Wallace et al., supra, at 529, col. 2. This reference also reveals that a 1987 paper by Webley and Hearn (J Endocrin. 112:449-457) reported that in vivo perfusion of melatonin to marmosets stimulated progesterone production by the marmoset corpus luteum. A 1986 Webley and Luck paper ([1986] J Reprod. Fert. 78:711-717) described in vitro melatonin-enhanced production of progesterone in human and bovine granulosa cells. This is in direct contrast to the results found for in vitro administration of melatonin to corpora lutea tissue according to the subject invention.
Melatonin has further been administered subcutaneously to sheep to alter the timing of the breeding season, and increased progesterone concentrations were observed. However, these studies utilized multiple, daily administrations of melatonin. Also, the aim of these treatments was not to induce increased progesterone, but to initiate reproductive cyclicity.
U.S. Pat. Nos. 5,272,141; 5,196,435; and 4,855,305 describe the use of melatonin as a contraceptive.
The subject invention, which can be distinguished from the teachings of the above references, relates to a different method of administering melatonin to effect enhanced pregnancy success. In particular, we have discovered that a single intravenous administration of melatonin to a female animal, and more particularly to a female of the Family Equidae, can provide for an improved uterine environment and corpus luteum which can enhance pregnancy success, contrary to the contraceptive use or cyclicity regulation described by certain of the prior references.
To our knowledge, use of melatonin according to the subject invention to enhance uterine environment, corpora lutea, or pregnancy success in an animal has not heretofore been described. Breeding of valuable animals, e.g., in the multimillion dollar horse-breeding industry, would derive substantial benefit from predictive and highly successful conception and pregnancy manipulation techniques. The only competing technology currently available in the horse-breeding industry is administration of progesterone exogenously, a technique that requires frequent (daily or bi-daily) and expensive ($1.00 to $3.00 daily) application for periods of up to 100 days. Multiple exogenous administrations of progesterone can maintain high circulating levels of progesterone to the extent that, if a pregnancy is misdiagnosed or is not maintained and progesterone administration is therefore withdrawn, the next normal estrous cycle is interrupted, disadvantageously preventing onset of xe2x80x9cheatxe2x80x9d or ovulation. A single administration of melatonin during proestrus or estrus allows for normal cycling to continue if pregnancy does not occur or if pregnancy is not maintained.
The subject matter of this invention pertains to a single administration of melatonin to an animal during the follicular phase (proestrus or estrus) of the estrous cycle. In particular, the subject method is advantageously used to enhance pregnancy success in mammals, including a human or other mammal in which a successful pregnancy is beneficial. The subject invention can be particularly advantageous when administered to breeding livestock, e.g., an animal in the Family Equidae, which includes horses, ponies, burros, asses, zebras, and the like, or the Family Ovidae, which includes sheep. Administration of melatonin at this time during the female cycle can result in the formation of an improved endocrine or uterine environment or corpus luteum, which unexpectedly maintains production of progesterone for a period of time which can enhance pregnancy success. In addition, melatonin administration according to the subject invention can improve the metabolism, e.g., increase estrogen production, by the conceptus membrane. Our data show that administration of melatonin within a specific time frame in the female cycle can alter the morphology of the corpus luteum, which likely occurs by altering the nuclear structure or function in the corpus luteum cell. The ultimate effect of an enhanced uterine environment in the establishment and maintenance of pregnancy can enhance the growth or viability of the conceptus.
More specifically, the subject technique utilizes administration of the indole-alkylamine melatonin (N-acetyl-5-methoxytryptamine) to enhance corpus luteum steroidogenesis. Advantageously, a single, intravenous administration of melatonin during the follicular phase (proestrus or estrus) can result in formation of a corpus luteum that is considerably enhanced, e.g., increases its production of progesterone. In one embodiment of the invention, melatonin administered to a mare or ewe during the follicular phase of the cycle can increase progesterone concentrations to stimulate uterine endometrial glandular secretion, thus enhancing the uterine environment for establishment or maintenance of pregnancy and the functional development of an embryo.
Currently, a very large percentage of horse breeders administer progesterone, itself, either as an intramuscular injection or through an orally active product. Administration of these products must be done daily, or at least every other day, for a period of up to about 100 days. Typically, the cost for such progesterone treatments is approximately $1.00 or $3.00 per day per animal. In addition, such treatments are usually initiated after pregnancy can be diagnosed by standard techniques, e.g., at day 18-20 of pregnancy. Early embryonic losses between conception and about day 20 of pregnancy can be as high as 25%. In view of the discoveries relating to the subject invention, such early embryonic losses may reflect progesterone concentrations which are inadequate to prepare optimal intra-uterine conditions. However, no effective method had heretofore been described which successfully achieves the desired intra-uterine conditions, or the improved corpus luteum or conceptus membrane. A single administration to an animal of an effective dose of melatonin, appropriately timed, can provide peripherally circulating progesterone concentrations approximately equal to or in excess of those generated with daily or every-other-day administration of progesterone. Compared to the multiple administrations of progesterone commonly used in the art, a single administration of melatonin not only can stimulate a corpus luteum to increase its function, e.g., production of progesterone, but also allows for the normal regression or demise of a corpus luteum if pregnancy does not occur or is not maintained, thereby allowing the normal estrous cycle to continue.
In another embodiment of the subject invention, melatonin is administered to an animal between about day 35-45, typically at about day 40, of pregnancy for enhancing secondary corpora lutea. The administration of melatonin at approximately day 40 of pregnancy can be given as a first treatment, i.e., to a pregnant animal not previously administered melatonin at proestrus or estrus immediately prior to conception. Alternatively, the administration of melatonin can be given as a second treatment to a pregnant animal initially administered melatonin at estrus or proestrus in accordance with the subject invention. Additional administrations of melatonin according to the subject invention can also be given during pregnancy in order to effect increased progesterone levels when desired. For example, in order to calm an active or hyperactive uterus during pregnancy to prevent spontaneous abortion, melatonin in the described dose can be administered to the animal during the first or second trimester of pregnancy, typically between day 40 and day 150 of pregnancy, and more preferably, between day 50 and day 120.
In yet another embodiment of the subject invention, melatonin can be administered as a method for reducing diestrus ovulations, thereby modifying behavior of an animal, e.g., producing a calming effect in performance animals that may be less controllable than normal during diestrus ovulations.